1. Field of the Invention
The present invention relates to a system for tracking a vehicle using an image of the vehicle photographed by a stationary camera placed on the road. In particular, the present invention relates to a vehicle search system and a vehicle search method capable of efficiently searching for a target vehicle, using vague information on a vehicle such as a vehicle color and the like as a clue, and a computer program product for realizing the vehicle search system and method.
2. Description of the Related Art
Conventionally, a technique of photographing a vehicle running on the road has been proposed. For example, JP2001-211383A discloses an apparatus for photographing a vehicle running on the road, considering environmental light.
A technique of recognizing a vehicle number from a vehicle image has also been proposed conventionally. For example, JP2001-273461A discloses an apparatus for reading and recognizing characters of a number plate with high precision from a vehicle image photographed on the road.
Furthermore, a technique of recognizing features such as a vehicle color, a vehicle type, and the like from a vehicle image, in addition to a vehicle number, has also been proposed. For example, JP2000-222673A discloses an apparatus for extracting a determination area for determining a coating color of a vehicle such as a hood from image data of the vehicle, and determining a color name of the determination area.
However, a particular vehicle can be hardly specified exactly using information on a vehicle to be searched for as a search condition. In most cases, a vehicle type and a vehicle color, as well as a vehicle number can only be expressed in a vague manner such as a “whitish sedan”.
Furthermore, even if a vehicle color and a vehicle type of a particular vehicle is given as a search condition, it is not easy to find out a vehicle matched with the search condition from a great amount of photographed and accumulated images. For example, in a camera placed at a point of a lot of traffic, the number of images of passing vehicles may amount to thousands of images. Even if the vehicle images can be classified based on the color as in the apparatus described in the above-mentioned JP2000-222673A, a considerable amount of time is required for displaying images of the corresponding vehicle color one by one (or by several images in such a range as to be displayed on a screen), and visually searching for a particular vehicle. Thus, by the time when an image of the particular vehicle is found out among the images photographed by the stationary camera, it is conceivable that the corresponding vehicle has already moved somewhere, and the direction in which the corresponding vehicle has moved cannot be specified. More specifically, it is conventionally difficult to specify a vehicle by a search based on uncertain information.